Case Study:
Repair of a Generator Stator with signs of
extensive end winding vibration and degradation.

ISSUE

During a major inspection of a 55375 KVA Generator, signs of extreme winding vibration and resonance issues were apparent.

After completing a visual inspection of the end winding
support systems, the following issues were identified and documented:

1. Extensive greasing and dusting on coil-to-coil ties, circuit ring to gunstock ties and circuit ring blocking
2. Extensive greasing and dusting of stator bars where they exited out of the slot
3. Broken and loose coil-to-coils ties
4. Cracked and, in some cases, broken gunstocks
5. Indications that circuit ring ties had cut into the insulation on the circuit rings

As part of the original scope, a wedge tap test was performed, which indicated loose wedges
in a large portion of the unit. This would also contribute to the extensive vibration issues
the unit was experiencing.

All other contracted “as found” electrical testing was completed and found to be satisfactory.

RECOMMENDATIONS

After discussions with the client, it was decided that a complete re-wedge and an end winding blocking modification should to be performed.

1. All ties found to have greasing or dusting were removed.
2. Damaged and broken gunstocks were removed.
3. Circuit rings and stator bars were checked for abrasion and surface damage.
4. All wedges and filler material were removed.
5. An extensive clean up was made on the end windings and slot sections to remove
   any remaining dust and grease.

RESOLUTION

1. New stator slot wedges and fillers were manufactured and installed.
2. New gunstocks were manufactured, installed and secured.
3. All coil-to-coil ties and circuit ring to gunstock ties were installed using industry-approved materials and methods.
4. Circuit rings were re-insulated in areas that had suffered abrasion.
5. New circuit ring blocking was installed in specific locations identified by our
   Engineering staff and braced using industry proven materials and methods.
6. End winding stiffening was performed using specific resins and epoxies.
7. Bump test was performed in order to confirm the repairs had improved the condition of the machine.
8. Final acceptance electrical testing was completed.
9. Painting of the unit and demobilization.

CONCLUSION

Although the condition of the end winding support systems were in a serious state of degradation, Sidewinders’ staff were able to steer the customer away from an imminent failure by performing a successful and very effective repair. This machine went back into service with its overall condition vastly improved and life significantly prolonged.